This invention relates generally to electrolytic apparatus, and more specifically relates to polymeric membranes of the type used in electrochemical cells, and to methods for manufacture of such membranes.
A cation exchange membrane comprising an inactive polymer film having sulfonated .alpha.,.beta.,.beta.-trifluorostyrene (hereinafter .alpha.,.beta..beta.-trifluorostyrene shall be referred as "TFS") as a graft chain is disclosed in U.S. Pat. No. 4,012,303, and has been used for the electrolysis of sodium chloride and fuel cells. The cation exchange membrane therein is prepared by graft-polymerizing TFS onto the inactive polymer film, and then sulfonating the grafted film.
Heretofore, the graft polymer membrane comprising the inactive polymer film and TFS graft-polymerized thereon has been prepared by dipping an inactive polymer film in or otherwise contacting it with a solution of TFS in an inert organic solvent, irradiating the film with Co or the like to graft-polymerize the TFS, and then sulfonating the grafted film. However, this method suffers from certain deficiencies, including that it is low in productivity and uneconomical, because the irradiation must be continued for 240 hours in order to produce a cation exchange membrane having a graft rate of about 15%. Furthermore since the TFS is also simultaneously irradiated, homopolymerization of the TFS, decrease of the graft rate and deterioration of the TFS occurs.